Since it is known that hole mobility is more than doubled on (110) silicon substrates compared with conventional (100) substrates, there is an increasing interest in manufacturing of high quality silicon substrates with (110) orientation. However, electron mobility is the highest on (100) substrates. Based on this knowledge, a new technology to fabricate high performance CMOS devices has been developed using hybrid silicon substrates with different crystal orientations, wherein pFETs are formed on a (110) oriented surface and nFETs are formed on a (100) surface and the different substrates are bonded.
For the manufacturing of such hybrid substrates with high quality, in particular the surface quality of the bonded substrates plays an important role. It is known from SOI substrates that the surface quality of the thin silicon layer on top of SOI substrates can suffer from some defects like HF-defects due to the presence of crystal defects being already present in the original CZ silicon material such as Crystal Oriented Pits (COP) and oxygen precipitations.
Therefore, some wafer manufacturers have developed special processes to fabricate (100) oriented silicon substrates with very low densities of COPs resulting in the effect that almost no defects such as HF-defects on final hybrid substrates were observed. It was further tried to form similarly bulk (110) silicon substrates without such defects, but these technologies are very expensive and show a very low yield due to low crystal growth. Beyond this, (110) oriented silicon is known to become easily rough and have problems in surface reconstruction because heat treatment of (110) substrates reveals low energy planes.